Flexible thermoplastic composite coupling and method of manufacture

ABSTRACT

A process for forming a flexible composite driveshaft includes providing a mandrel having a rigid region and a compressible region, applying fiber tape to the mandrel using automated fiber placement with in-situ laser curing in the rigid region and without in-situ laser curing the compressible region, and compressing the fiber tape and compressible material in the compressible region to form diaphragms that extend radially outward to a diameter that is at least twice the size of a diameter of the composite driveshaft in the rigid region.

BACKGROUND

The present disclosure is related generally to driveshafts and moreparticularly to a method for manufacturing a flexible compositedriveshaft.

Driveshafts are used to connect components to a drive input. Knownapplications include but are not limited to driveshafts used to drivepropellers in aerospace applications. Driveshafts transmit primarilytorque and rotation. Driveshafts are generally cylindrical bodies, whichcan include multiple flexible elements in series that provide bendingand/or axial compliances to accommodate angular and axial misalignmentand mass imbalance.

Composite driveshafts can provide increased strength and reduced weightas compared to conventional metal designs. However, driveshaft designsand, particularly, the geometry of flexible elements, are limited bycurrent composite manufacturing methods.

SUMMARY

In one aspect, a process for forming a flexible composite driveshaftincludes providing a compressible mandrel, applying a fiber tape to thecompressible mandrel using automated fiber placement to form apreliminary composite driveshaft having a longitudinal axis, andreducing a diameter of the composite driveshaft to form first and seconddiaphragms. The preliminary composite drive shaft includes a firstregion extending longitudinally and having a substantially constantfirst diameter and a second region extending longitudinally from thefirst region and protruding radially outward from the first region in amound shape. The mound shape is defined by a diameter that increasesradially as a function of axial position from the first diameter at afirst end adjacent to the first region to a radially outermost seconddiameter at a central portion of the second region and decreasesradially as a function of axial position from the central portion to thefirst diameter at a second end. The diameter of a section of the secondregion is reduced to divide the second region into first and seconddiaphragms, each of the first and second diaphragms having a diametergreater than the first diameter.

In another aspect, a flexible composite driveshaft formed by automatedfiber placement includes a first region extending longitudinally aboutan axis and having a substantially constant first diameter and a secondregion adjacent to the first region and including first and seconddiaphragms each extending radially outward from the first region about acircumference of the driveshaft and each having second diameter that isat least twice the size of the first diameter.

In yet another aspect, a process for forming a flexible compositedriveshaft includes providing a mandrel having a compressible material,applying fiber tape to the compressible material using automated fiberplacement, and compressing the fiber tape and compressible material toform diaphragms. The mandrel includes a rigid cylinder, one or morefirst rigid members and one or more second rigid members positionedcircumferentially about a portion of the outer surface of the rigidcylinder and separated from one another along a longitudinal axis of thedriveshaft, and a compressible material provided around and between thefirst and second rigid members. A plurality of strips of fiber tape areapplied to a first longitudinally extending region of the mandreladjacent to the one or more first and second rigid members usingautomated fiber placement with in-situ laser curing. A plurality ofstrips of fiber tape are applied to a second longitudinally extendingregion of the mandrel comprising the one or more first and second rigidmembers and compressible material using automated fiber placementwithout in-situ laser curing. The plurality of strips of fiber tape andcompressible material are compressed to conform to the one or more firstand second rigid members.

The present summary is provided only by way of example, and notlimitation. Other aspects of the present disclosure will be appreciatedin view of the entirety of the present disclosure, including the entiretext, claims, and accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an axial cross-sectional representation of a mandrel forfabrication of a flexible composite driveshaft using automated fiberplacement (AFP).

FIG. 2 is an axial cross-sectional representation of a preliminaryflexible composite driveshaft formed on the mandrel of FIG. 1.

FIG. 3 is an isometric view of one embodiment of fiber layers of thepreliminary flexible composite driveshaft of FIG. 2 with a portion ofoverlying layers removed to show underlying layers.

FIG. 4 is an axial cross-sectional representation of a flexiblecomposite driveshaft following compression of the preliminary flexiblecomposite driveshaft of FIG. 2.

FIG. 5 is a radial cross-sectional representation of an outer diameterof the mandrel of FIG. 4 taken along the 5-5 line.

FIG. 6 is an axial cross-sectional representation of the flexiblecomposite driveshaft of FIG. 4, following removal of the mandrel.

FIG. 7 is a flow chart of a method for forming a flexible compositedriveshaft.

While the above-identified figures set forth embodiments of the presentinvention, other embodiments are also contemplated, as noted in thediscussion. In all cases, this disclosure presents the invention by wayof representation and not limitation. It should be understood thatnumerous other modifications and embodiments can be devised by thoseskilled in the art, which fall within the scope and spirit of theprinciples of the invention. The figures may not be drawn to scale, andapplications and embodiments of the present invention may includefeatures, steps and/or components not specifically shown in thedrawings.

DETAILED DESCRIPTION

Automated fiber placement (AFP) can be used to produce high performancecomposite components in which the positioning of fibers or fiber pathscan be locally optimized to meet varying load requirements. The benefitsprovided by AFP are desirable in the manufacture of compositedriveshafts; however, the size of the fiber placement head restricts thegeometry of the driveshaft that can be formed by the direct, one-step,AFP layup alone. Multiple flexible elements provided in series providebending and/or axial compliances to accommodate angular and axialmisalignment and mass imbalance. A relatively sharp angle or smallcorner radius is required between flexible elements, but such smallradii cannot be produced with AFP technology.

The disclosed method of manufacture utilizes a combination of rigid andcompressible mandrel elements that provide a gradual variation in shaftdiameter to allow for fiber placement using AFP. Rigid dissoluble doublemound members can be positioned around a circumference of a rigidcylinder and separated and surrounded by a compressible material form toprovide the gradual variation in surface geometry required for AFP. Oncefiber layup is complete, the fiber layers overlaying the compressiblematerial can be compressed to conform to a shape of the mound members toproduce large diameter flexible elements having sharp corner or smallradius transitions at the shaft. A two-step curing process is used inwhich the uniform diameter shaft portion of the driveshaft islaser-cured in-situ during the AFP process. The laser can be turned offduring fiber placement in regions including the compressible material toprovide for subsequent deformation. The deformed region can besubsequently cured and all mandrel elements can be removed.

Flexible driveshafts can have one or more flexible elements (ordiaphragms), generally defined by a change in a size of an outerdiameter or radial extent of the shaft with a transition radius capableof accommodating bending during operation. Shaft bending flexibility canbe increased by increasing the number of flexible elements on the shaftor a diameter of the flexible elements. Two or more flexible elementsare illustrated in each of the embodiments disclosed herein. However, itwill be understood that a composite driveshaft manufactured according tothe present disclosure can have a single flexible element or moreflexible elements than illustrated, each defined by an increase in theouter diameter or radial extent of the shaft. A small radius or sharpcorner between flexible elements and on either side of a single flexibleelement in a transition region where the flexible element meets theshaft can be required to accommodate bending. As used herein, “sharpcorner” refers to a minimum, but non-zero radius. A minimum radius sizecan be limited by a size and orientation of the fibers used to form thecomposite shaft and can be set to prevent or reduce fiber breakage. Thesize of the radius can vary depending on the application, appliedmaterials, and fabrication specifics. The method of the presentdisclosure can be used to create constant and/or variable radii of anysize limited only by a need to limit fiber breakage and is not limitedto the designs illustrated herein.

FIG. 1 is an axial cross-sectional representation of mandrel 10 forfabrication of one embodiment of a flexible composite driveshaft usingAFP. Mandrel 10 includes a rigid cylinder 12, rigid members 14 a-14 d,and compressible material 15. Cylinder 12 and rigid members 14 a-14 dcan be formed from any material suitable for providing a rigid andremovable form for AFP as known in the art, including but not limited totool steel and hard plastic. Rigid members 14 a-14 d generally define afinal geometry of the flexible elements of the driveshaft. Asillustrated in FIG. 1, rigid members 14 a-14 d can be arranged inaxially-separated pairs about a circumference of cylinder 12, providingtwo radially extending rings around cylinder 12 at each end of cylinder12. In alternative embodiments, rigid members can be arranged in groupsof more than two to provide a driveshaft with additional flexibleelements, or can be arranged to provide a single flexible member 44(shown in FIG. 6) at each end of the drive shaft. Rigid members 14 a-14d can have a non-uniform cross-section as shown in FIG. 2. The diameterof rigid members 14 a-14 d can be varied to improve performance.Preferably, the diameter of rigid members 14 a-14 d is at least twicethe diameter of cylinder 12. It will be understood by one of ordinaryskill in the art that rigid members 14 a-14 d can be positioned andshaped as needed to provide the driveshaft with sufficient bendingflexibility during operation.

Each of rigid members 14 a-14 d can include a plurality of segments (notshown) that are circumferentially arranged to provide a substantiallysolid ring around cylinder 12. The geometry of the segments can beconfigured to allow for the segments to fall into the hollow centralportion of the shaft upon removal of cylinder 12 following final curingof the flexible elements. In alternative embodiments, rigid members 14a-14 d can be a dissolvable material that can be removed with washing orother known methods.

Compressible material 15 can be applied around rigid members 14 a-14 dto form a single mound shaped compressible form over each rigid memberpair 14 a, 14 b and 14 c, 14 d. Compressible material 15 can be arrangedto provide a gradual increase or transition in shaft diameter, therebyremoving all sharp or small radius corner, as needed for fiber placementusing AFP. As illustrated in FIG. 1 the mound-shaped compressible formextends longitudinally along cylinder 12 and protrudes radially outwardfrom cylinder 12. The mound shape is defined by a diameter thatincreases radially as a function of axial position from a first diameterd₁ at cylinder 12 at one end 16 to a radially outermost second diameterd₂ at a central portion 17 of the mound and decreases radially as afunction of axial position from the central portion 17 to the firstdiameter d₁ at a second end 18, thereby forming gradual transitionregions between cylinder 12 and rigid members 14 a-14 d.

Compressible material 15 can be a form or mold shaped to fit over rigidmember pair 14 a, 14 b and 14 c, 14 d. Compressible material 15 can be adissolvable plastic, meltable metal, or other material capable ofproviding sufficient rigidity for fiber layup while also beingsubstantially compressible, and removable upon final curing of thedriveshaft. Compressible material that can be pressed to closely conformto the outer surfaces of rigid members 14 a-14 d is preferable.

In some embodiments, an additional stiffener member 19 can be providedat the top of adjacent rigid members 14 a, 14 b and 14 c, 14 d to coverthe grooves formed between the rigid member pairs. Stiffener member 19is made of a compressible material capable of conforming to the shape ofthe outer surfaces of rigid members 14 a-14 d. In some embodiments,compressible material 15 that would be otherwise provided in the groovesbetween adjacent rigid members 14 a, 14 b and 14 c, 14 d can beeliminated if stiffener member 19 is present.

FIG. 2 is an axial cross-sectional representation of a preliminaryflexible composite driveshaft 20 formed on mandrel 10. Preliminarycomposite driveshaft 20 is formed by applying a thermoplastic fiber tapeto mandrel 10 using AFP. The fiber tape can be wrapped around mandrel 10or otherwise placed to cover mandrel 10 with AFP tool 22. Multiplelayers of fiber tape can be applied to mandrel 10 to increase athickness of preliminary composite driveshaft 20. It will be understoodby one of ordinary skill in the art that fiber placement, fiberdirection, and layering of fiber tape, can be optimized to meet localload conditions and can vary depending on the intended application.

FIG. 3 is an isometric view of a non-limiting, simplified embodiment ofa fiber layup of preliminary flexible composite driveshaft 20. Asillustrated in FIG. 3, strips of fiber tape 24 can be arranged inmultiple layers 26, 28, 30, 32 (FIG. 3 shows a portion of overlyinglayers 28, 30, 32 removed to show underlying layers). Fiber tape 24 canbe arranged in a single direction in each layer 26, 28, 30, 32 andarranged to fully or partially cover mandrel 10. As illustrated, theorientation of fiber tape 24 in each layer can vary. Fiber tape 24 canbe oriented in a longitudinal direction (zero degrees) to providebending stiffness to meet dynamic response requirements. Additionally,fiber tape 24 can be arranged in a circumferential direction (90degrees), and at any+/−angle between zero and 90 degrees. As illustratedin FIG. 3, fiber tape 24 is oriented at both+45 and −45 degrees,although it will be understood by one of ordinary skill in the art thatthe orientation of fiber tape 24 can be optimized to accommodatedifferent load conditions in operation.

Fiber tape 24 can be a thermoplastic unidirectional fiber tape that caninclude but is not limited to carbon, glass, organic fibers, or any ofcombination thereof, as known in the art, preimpregnated with athermoplastic resin matrix. The use of a thermoplastic fiber tape 24 ispreferable to thermoset fiber tapes, which are irreversibly hardened bycuring. The thermoplastic fiber tape 24 provides enhanced capability toform complex geometries and appears to have greater tolerance to damageas compared to thermoset materials.

During AFP, laser 34 on the AFP tool can be turned off and on toselectively cure fiber tape 24. The laser can be turned on to cure fibertape 24 in regions 36 of the driveshaft formed directly on cylinder 12and not requiring further deformation. The laser can be turned off toavoid curing fiber tape 24 in regions 38 of the driveshaft overlayingcompressible material 15 to allow for subsequent deformation. Regions 36extend longitudinally and can have a substantially constant diameter.Regions 38 extend longitudinally from regions 36 and protrude radiallyoutward from regions 36 in a mound shape. In some embodiments, partialcuring may be required in select locations of the compressible region toadhere strips of fiber tape. In some embodiments, a temporary adhesivematerial may be applied to retain placement of fiber strips 24 or fiberlayup can be configured to minimize the number or location of loosefiber strips 24.

FIG. 4 is an axial cross-sectional representation of flexible compositedriveshaft 40 following compression of preliminary flexible compositedriveshaft 20 but before mandrel 10 has been removed. One or moreforming elements 42 can be placed around an outer diameter ofpreliminary composite driveshaft 10 to compress preliminary compositedriveshaft 20 in the radial inward direction around the fullcircumference to produce reduced radius r₁ or a sharp angle betweenadjacent rigid members 14 a, 14 b and 14 c, 14 d, thereby formingflexible elements or diaphragms 44 (labeled in FIG. 6) and a reducedtransition radius r₂ or sharp angle on either side of adjacent rigidmember pairs 14 a, 14 b and 14 c, 14 d. A load directed radially inwardtoward axis A can be applied to elements 42 to compress the outerdiameter in a location generally corresponding to central section 17 andin the transition regions between ends 16 and 18 and central section 17(shown in FIG. 1). Elements 42 can be positioned between adjacent rigidmembers 14 a, 14 b and 14 c, 14 d and in transition regions on eitherside of rigid members 14 a-14 d. Elements 42 can be configured to fitsecurely between rigid members 14 a-14 d and have a geometry thatsubstantially matches a desired final geometry (i.e., r or sharp angle)formed between adjacent rigid members 14 a, 14 b and 14 c, 14 d.Elements 42 can be multi- or two-piece split clamps as known in the artor other suitable clamping elements or forming molds known to providesufficient compression and which can be used during a subsequent curingprocess to retain compression.

Compression of preliminary composite driveshaft 20 between rigid memberpairs 14 a, 14 b and 14 c, 14 d takes fiber layers from a largestdiameter d₃ to a smallest diameter d₄. Preferably, diameter d₃ is atleast twice the size of diameter d₄. Fiber tape 24 oriented in acircumferential direction or generally circumferential direction will betoo long for the smaller diameter d₄. As such, compression will causewrinkling of the fiber tape 24 in this region. In some embodiments, asection of cylinder 12 corresponding in position to the central portionof the second region or groove between adjacent rigid members 14 a, 14 band 14 c, 14 d can have a wavy or undulating outer surface 46 defined bycircumferentially spaced indentations 48, as illustrated in FIG. 5. FIG.5 is a schematic radial cross-sectional representation of outer diameter46 of the composite driveshaft 40 of FIG. 4 taken along the 5-5 line.Indentations 48 can accommodate the wrinkles or folds formed uponcompression by one or more of the strips of fiber tape 24 oriented inthe circumferential direction. When cured, the indentations remain inplace and accommodate the extra fiber or tape length. To a smallerextent, excess fiber tape length can be present on the sloping area oneither side of each adjacent rigid member pair 14 a, 14 b and 14 c, 14d. However, layout of the multiple layers can generally accommodate themismatch in these regions. Fiber tape 24 oriented in the longitudinaldirection or at ±45 degrees can generally conform to the shape of thegroove between adjacent rigid members 14 a, 14 b and 14 c, 14 d providedthe outer diameter d₂ of compressible form 15 is no excessively large incomparison to the final compressed diameter. Additional care in mandreldesign may be required to limit fiber breakage during compression. Forexample, the size of compressible form 15 over rigid member pairs 14 a,14 b and 14 c, 14 d can be sized (i.e., d₂) to provide sufficient fibertape length to reach the bottom of the groove formed between adjacentrigid members 14 a, 14 b and 14 c, 14 d, thereby limiting a need forstretching of fiber tape 24 during compression.

Following compression, the modified sections of flexible elements 44(labeled in FIG. 6) of preliminary driveshaft 20 can be cured in an ovenas known in the art with mandrel 10 and clamping or forming elements 42in place. Use of an autoclave, which can be required in some prior artmethods, is unnecessary in the disclosed process.

When the formation and curing of flexible composite driveshaft 40 iscomplete, all parts of mandrel 10 can be removed as previouslydescribed, leaving the hollow flexible composite driveshaft 40. FIG. 6is a schematic axial cross-sectional representation of flexiblecomposite driveshaft 40, with flexible elements 44, following removal ofmandrel 10.

FIG. 7 is a flow chart of a method for forming a flexible compositedriveshaft 40. A previously described, mandrel 10 can be assembled byproviding a rigid cylinder 12 (step 102), attaching one or more rigidmembers 14 a-14 d circumferentially about an outer surface of cylinder12 (step 104), and applying a compressible form or material 15 aroundand between adjacent rigid members 14 a, 14 b and 14 c, 14 d (step 106).Fiber tape 24 is applied to mandrel 10 using AFP with in-situ lasercuring in regions formed directly on cylinder 12 (step 108) and withoutin-situ curing in regions containing the compressible form (step 110). Alaser used for in-situ curing can be turned on to cure fiber tape 24 andcan be turned off to leave fiber tape 24 uncured. Fibers are compressedaround rigid members 14 a-14 d to form flexible elements 44 (step 112).The uncured region is subsequently cured in an oven while maintainingcompression (step 114). Once the flexible composite driveshaft is fullyshaped and cured, all parts of mandrel 10 are removed, for example, byphysical extraction, washing or melting of material, or other methodsknown in the art (step 115).

The disclosed method of manufacture capitalizes on the advantagesprovided by thermoplastic AFP, while overcoming the limitations ofcurrent AFP technology to achieve small radius or sharp cornertransitions required in flexible driveshaft design.

Discussion of Possible Embodiments

The following are non-exclusive descriptions of possible embodiments ofthe present invention.

A process for forming a flexible composite driveshaft includes providinga compressible mandrel, applying a fiber tape to the compressiblemandrel using automated fiber placement to form a preliminary compositedriveshaft having a longitudinal axis, and reducing a diameter of thecomposite driveshaft to form first and second diaphragms. Thepreliminary composite drive shaft includes a first region extendinglongitudinally and having a substantially constant first diameter and asecond region extending longitudinally from the first region andprotruding radially outward from the first region in a mound shape. Themound shape is defined by a diameter that increases radially as afunction of axial position from the first diameter at a first endadjacent to the first region to a radially outermost second diameter ata central portion of the second region and decreases radially as afunction of axial position from the central portion to the firstdiameter at a second end. The diameter of a section of the second regionis reduced to divide the second region into first and second diaphragms,each of the first and second diaphragms having a diameter greater thanthe first diameter.

The process of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations additional components, and/or steps:

A further embodiment of the foregoing process can include curing thefirst region during automated fiber placement with a laser and leavingthe second region substantially uncured during automated fiberplacement.

A further embodiment of any of the foregoing processes, wherein leavingthe second region substantially uncured can include turning off thelaser during automated fiber placement.

A further embodiment of any of the foregoing processes, wherein reducinga diameter of a section of the second region can include applyingpressure to the section with a forming element.

A further embodiment of any of the foregoing processes, whereinproviding the compressible mandrel can include providing a rigidcylinder, wherein an outer surface of the rigid cylinder provides asurface for automated fiber placement in the first region, positioningone or more first rigid members and one or more second rigid memberscircumferentially about a portion of the outer surface of the rigidcylinder, wherein the one or more first and one or more second rigidmembers are configured to provide a shaping form for the first or seconddiaphragm, and providing a compressible material between and on eitherside of the first and second rigid members, wherein the compressiblematerial provides a surface for automated fiber placement in the secondregion.

A further embodiment of any of the foregoing processes can furtherinclude applying pressure to end sections of the second region about acircumference to reduce a transition radius between the first and secondregions.

A further embodiment of any of the foregoing processes, wherein therigid cylinder can have a section corresponding in position to thecentral portion of the second region, the section having an outersurface defined by circumferentially spaced indentations.

A further embodiment of any of the foregoing processes, wherein applyingthe fiber tape can include applying a plurality of strips ofunidirectional fiber tape in a longitudinal direction and acircumferential direction and wherein the indentations accommodatewrinkles formed upon compression by one or more of the plurality ofstrips of tape oriented in the circumferential direction.

A further embodiment of any of the foregoing processes can furtherinclude providing a clamping member to the central portion to applypressure to the central portion during the curing process.

A further embodiment of any of the foregoing processes can furtherinclude removing the rigid cylinder, the one or more first and secondrigid members, and the compressible material following curing of thesecond region.

A flexible composite driveshaft formed by automated fiber placementincludes a first region extending longitudinally about an axis andhaving a substantially constant first diameter and a second regionadjacent to the first region and including first and second diaphragmseach extending radially outward from the first region about acircumference of the driveshaft and each having second diameter that isat least twice the size of the first diameter.

The flexible composite driveshaft of the preceding paragraph canoptionally include, additionally and/or alternatively, any one or moreof the following features, configurations and/or additional components:

A further embodiment of the foregoing flexible composite driveshaft,wherein the first and second regions can each include a plurality ofstrips of unidirectional fiber tape, the plurality of strips oriented ina longitudinal direction and in a circumferential direction.

A further embodiment of any of the foregoing flexible compositedriveshafts, wherein at least one of the circumferentially-orientedstrips of unidirectional fiber tape positioned between the first andsecond diaphragms can include a plurality of folds formed about thecircumference of the driveshaft.

A further embodiment of any of the foregoing flexible compositedriveshafts, wherein the plurality of strips of unidirectional fibertape can be unwoven and arranged in a plurality of stacked layers.

A process for forming a flexible composite driveshaft includes providinga mandrel having a compressible material, applying fiber tape to thecompressible material using automated fiber placement, and compressingthe fiber tape and compressible material to form diaphragms. The mandrelincludes a rigid cylinder, one or more first rigid members and one ormore second rigid members positioned circumferentially about a portionof the outer surface of the rigid cylinder and separated from oneanother along a longitudinal axis of the driveshaft, and a compressiblematerial provided around and between the first and second rigid members.A plurality of strips of fiber tape are applied to a firstlongitudinally extending region of the mandrel adjacent to the one ormore first and second rigid members using automated fiber placement within-situ laser curing. A plurality of strips of fiber tape are applied toa second longitudinally extending region of the mandrel comprising theone or more first and second rigid members and compressible materialusing automated fiber placement without in-situ laser curing. Theplurality of strips of fiber tape and compressible material arecompressed to conform to the one or more first and second rigid members.

The process of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations additional components, and/or steps:

A further embodiment of the foregoing process can include curing thesecond region, wherein a clamping element is provided to maintaincompression during curing.

A further embodiment of any of the foregoing processes, wherein therigid cylinder can have a section corresponding in position to alocation between the first and second rigid members and can have anouter surface defined by circumferentially spaced indentations.

A further embodiment of any of the foregoing processes, wherein applyingthe fiber tape can include applying a plurality of strips ofunidirectional fiber tape in a longitudinal direction and acircumferential direction and wherein the indentations can accommodatewrinkles formed upon compression by one or more of the plurality ofstrips of tape oriented in the circumferential direction

A further embodiment of any of the foregoing processes can includeremoving the rigid cylinder, the one or more first and second rigidmembers, and the compressible material following curing of the secondregion.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

The invention claimed is:
 1. A process for forming a flexible compositedriveshaft, the process comprising: applying a fiber tape to acompressible mandrel using automated fiber placement to form apreliminary composite driveshaft having a longitudinal axis, thepreliminary composite drive shaft comprising: a first region extendinglongitudinally and having a substantially constant first diameter; and asecond region extending longitudinally from the first region andprotruding radially outward from the first region in a mound shapedefined by a diameter that increases radially as a function of axialposition from the first diameter at a first end adjacent to the firstregion to a radially outermost second diameter at a central portion ofthe second region and decreases radially as a function of axial positionfrom the central portion to the first diameter at a second end; andreducing a diameter of a section of the second region to divide thesecond region into first and second diaphragms, each of the first andsecond diaphragms having a diameter greater than the first diameter. 2.The process of claim 1, and further comprising: curing the first regionduring automated fiber placement; and leaving the second regionsubstantially uncured during automated fiber placement.
 3. The processof claim 2, wherein leaving the second region substantially uncuredcomprises turning off a laser during automated fiber placement.
 4. Theprocess of claim 3, wherein reducing a diameter of a section of thesecond region comprises applying pressure to the section with a formingelement.
 5. The process of claim 1, wherein providing the compressiblemandrel comprises: providing a rigid cylinder, wherein an outer surfaceof the rigid cylinder provides a surface for automated fiber placementin the first region; positioning one or more first rigid members and oneor more second rigid members circumferentially about a portion of theouter surface of the rigid cylinder, wherein the one or more first andone or more second rigid members are configured to provide a shapingform for the first or second diaphragm; and providing a compressiblematerial between and on either side of the first and second rigidmembers, wherein the compressible material provides a surface forautomated fiber placement in the second region.
 6. The process of claim5, and further comprising applying pressure to end sections of thesecond region about a circumference to reduce a transition radiusbetween the first and second regions.
 7. The process of claim 5, whereinthe rigid cylinder has a section corresponding in position to thecentral portion of the second region, the section having an outersurface defined by circumferentially spaced indentations.
 8. The processof claim 5, wherein applying the fiber tape comprises applying aplurality of strips of unidirectional fiber tape in a longitudinaldirection and a circumferential direction and wherein the indentationsaccommodate wrinkles formed upon compression by one or more of theplurality of strips of tape oriented in the circumferential direction.9. The process of claim 5, and further comprising curing the secondregion.
 10. The process of claim 9, and further comprising providing aclamping member to the central portion to apply pressure to the centralportion during the curing process.
 11. The process of claim 10, andfurther comprising removing the rigid cylinder, the one or more firstand second rigid members, and the compressible material from theflexible composite driveshaft following curing of the second region. 12.A process for forming a flexible composite driveshaft, the processcomprising: providing a mandrel comprising: a rigid cylinder; one ormore first rigid members and one or more second rigid members, each ofthe one or more first and second rigid members positionedcircumferentially about a portion of the outer surface of the rigidcylinder, wherein the one or more first rigid member are separated fromthe one or more second rigid members along a longitudinal axis of thedriveshaft; and a compressible material provided around and between thefirst and second rigid members; applying a plurality of strips of fibertape to a first longitudinally extending region of the mandrel adjacentto the one or more first and second rigid members using automated fiberplacement with in-situ laser curing; applying the plurality of strips offiber tape to a second longitudinally extending region of the mandrelcomprising the one or more first and second rigid members andcompressible material using automated fiber placement without in-situlaser curing; and compressing the plurality of strips of fiber tape andcompressible material to conform to the one or more first and secondrigid members.
 13. The process of claim 12, and further comprisingcuring the second region, wherein a clamping element is provided tomaintain compression during curing.
 14. The process of claim 13, whereinthe rigid cylinder has a section corresponding in position to a locationbetween the first and second rigid members and has an outer surfacedefined by circumferentially spaced indentations.
 15. The process ofclaim 14, wherein applying the fiber tape comprises applying a pluralityof strips of unidirectional fiber tape in a longitudinal direction and acircumferential direction and wherein the indentations accommodatewrinkles formed upon compression by one or more of the plurality ofstrips of tape oriented in the circumferential direction.
 16. Theprocess of claim 13, and further comprising removing the rigid cylinder,the one or more first and second rigid members, and the compressiblematerial following curing of the second region.